B100 - W24 - Stud - T9 - Excretory System .pdf

Excretory System Excretory System Functions Excretion of Osmoregulation Nitrogenous Waste Osmoregulation balances the uptake and loss of water and solutes Osmoregulation is based largely on controlled movement of solutes and water between body’s internal fluids and the external environment. Therefor...

Excretory System Excretory System Functions Excretion of Osmoregulation Nitrogenous Waste Osmoregulation balances the uptake and loss of water and solutes Osmoregulation is based largely on controlled movement of solutes and water between body’s internal fluids and the external environment. Therefore, osmoregulation is used to keep the bodily fluid from being too diluted or too concentrated Osmoregulation balances the uptake and loss of water and solutes All animals face the same need to balance water uptake and loss…as you recall, water enters and leaves cells by osmosis. Osmosis occurs when two solutions separated by a selectively permeable membrane differ in osmolarity. ✓Osmolarity = total solute concentration of a solution expressed as number of milliosmoles (mOSm) of solute per litre ✓The osmolarity of human blood is about 300 mOsm/L, while seawater has an osmolarity of about 1,000 mOsm/L Therefore, the total solute concentration of a solution determines the movement of water across a selectively permeable membrane. If two solutions are iso-osmotic, the movement of water is equal in both directions (so the net movement of water will be zero) If two solutions differ in osmolarity, the net flow of water is from the hypo-osmotic to the hyper-osmotic solution Higher solute concentration Lower free water concentration Lower solute concentration Higher free water concentration Excretion of Nitrogenous Waste Nitrogenous wastes in animals include three molecules: o Ammonia o Urea o Uric acid Humans excrete nitrogen through urea like many other mammals. Kidneys are the main excretory organ in humans As the major excretory organ in humans (and other mammals), the kidney: o Osmoregulates the body’s internal environment by controlling the amount of water and salts excreted through the urine. o Excretes nitrogenous wastes (urea) from the body through the urine. However, several other organs are also involved in excretion: o Water and electrolytes are lost through sweat glands in the skin o Lungs in charge of removing carbon dioxide o Liver breaks down toxic substances in the blood, as well as produces urea. o Large intestine (colon) removes solid waste and some water in the form of feces. Kidneys Latim: renibus Kidneys are two bean-shaped organs located just below the rib cage (more specifically located below the liver). Each kidney is supplied with blood by a renal artery and drained by a renal vein. Kidneys Latim: renibus Urine exits each kidney through a muscular duct called the ureter (in adult humans, one ureter is 25-30 cm long). Both ureters drain into a common urinary bladder, and urine is expelled through the urethra. Kidneys Latim: renibus The mammalian kidney has two distinct regions: an outer renal cortex and an inner renal medulla ✓ The renal medulla is divided into eight or more triangular-shaped sections called renal pyramids Kidneys Latim: renibus The renal pyramids contain the nephrons, which are the functional unit of the kidney. ü The urine is produced by the nephrons Each minor calyx collects urine from one renal medulla while each major calyx collects urine from minor calyces…the renal pelvis collects urine from all major calyces. The nephron is the functional unit of the kidney The nephron consists of a single long tubule and a ball of capillaries called the glomerulus Bowman’s capsule surrounds and receives filtrate from the glomerulus capillaries Practice Questions The urinary bladder is responsible for the production of urine. The urinary bladder is responsible for the production of urine. False Urine is produced in the nephron located in the kidney. The urinary bladder stores the urine The excretory system is closely connected to the circulatory system to remove waste products from the blood. The excretory system is closely connected to the circulatory system to remove waste products from the blood. True The urethra is the tube that carries urine from the kidneys to the urinary bladder. The urethra is the tube that carries urine from the kidneys to the urinary bladder. False The ureter carries the urine from the kidneys to the bladder. The urethra is the tube responsible for expelling urine, connecting the urinary bladder to the exit (urinary pore). Electrolytes can be eliminated in the sweat by the skin Electrolytes can be eliminated in the sweat by the skin True (2 marks) Why is it important to maintain the balance between water intake and water excretion in the excretory system? (2 marks) Why is it important to maintain the balance between water intake and water excretion in the excretory system? Keeping an adequate balance between water intake and excretion is important in the maintenance of blood osmolarity (1 mark). If this balance is disrupted, it can cause RBC to lyse or crenate, impacting oxygen transportation and the whole organism's physiology (1 mark) Label the four parts of the kidney. 3 2 1 4 Label the four parts of the kidney. renal cortex renal pelvis ureter renal medulla (2 marks) The following five structures participate in urine storage and elimination: ureter, urethra, renal pelvis, bladder, and calyx. Using these structures, correctly order the flow of urine after it exits the nephron. (2 marks) The following five structures participate in urine storage and elimination: ureter, urethra, renal pelvis, bladder, and calyx. Using these structures, correctly order the flow of urine after it exits the nephron. Calyx Renal pelvis Ureter Bladder Urethra The nephron is the functional unit of the kidney The nephron consists of a single long tubule and a ball of capillaries called the glomerulus Bowman’s capsule surrounds and receives filtrate from the glomerulus capillaries How many nephrons are in each adult human kidney? How many nephrons are in each adult human kidney? About 1 million (with a total tubule length of 80 km) Kidneys use filtration, reabsorption and secretion to produce urine ✓Filtration – involves transfer of soluble components (like water and waste) from blood (glomerulus) across Bowman’s capsule and into nephron ✓Reabsorption – involves absorption of molecules, ions, and water necessary for the body to maintain homeostasis from inside the nephron back into blood. ✓Secretion – involves transfer of molecules (like hydrogen ions, drugs, and urea) from blood into nephron. Filtration Occurs at renal corpuscle (made up of both the glomerulus and Bowman’s capsule) efferent arteriole Filtration occurs as blood pressure forces fluid from the blood in the glomerulus to lumen of Bowman’s capsule The fenestrated endothelium of capillaries (i.e., pores), along with specialized capsule cells called podocytes (these cells have membranes that fold into a series of slits and ridges), are permeable to small molecules but not to blood cells or plasma proteins Small molecules that can be filtered include water, salts, glucose, amino acids, vitamins, and nitrogenous wastes (i.e., urea) afferent arteriole Pathway of the filtrate in nephron From Bowman’s capsule, the filtrate passes through nephron in following order: ‒ Proximal convoluted tubule à descending loop of Henle à ascending loop of Henle (thin segment) à ascending loop of Henle (thick segment) à distal convoluted tubule à collecting duct Descending arm of Ascending arm of Loop of Henle (thick segment) Ascending arm of Loop of Henle (thin segment) Blood vessels associated with nephron Each nephron is supplied with blood by an afferent arteriole = a branch of the renal artery that divides into the capillaries of the glomerulus The capillaries converge as they leave the glomerulus, forming an efferent arteriole Vasa recta Blood vessels associated with nephron The efferent arteriole subdivides again, forming the peritubular capillaries, which surround the proximal and distal convoluted tubules Additional capillaries extend downward forming the vasa recta, which serve the loop of Henle Vasa recta The nephron is organized for stepwise processing of blood filtrate Proximal Convoluted Tubule Reabsorption of ions (K+, Na+, Cl-, HCO3-), water moves in by osmosis), and nutrients (glucose, amino acids, vitamins) takes place ‒ Note: about 90% of the HCO3- is reabsorbed (contributes to pH balance in body fluids like the blood) These molecules are transported actively or passively from the filtrate into peritubular capillaries Some toxic materials (drugs and other poisons) are secreted into the + filtrate, as well as H and NH3 Overall , the filtrate volume decreases since most of the filtrate is reabsorbed here (~65% of it) Osmolarity of filtrate in nephron just after proximal tubule is about 300 mOsm/L (so filtrate is iso-osmotic to the blood) Descending limb of the Loop of Henle Thick segment Reabsorption of water continues through channels formed by aquaporin proteins (however, transport epithelium not permeable to salt) Filtrate becomes very concentrated with solute Osmolarity in descending arm changes from 300 mOsm/L at beginning to 1,200 mOsm/L at end (so filtrate in nephron is hyper-osmotic to the blood) Descending limb Ascending limb Ascending limb of the Loop of Henle Transport epithelium is permeable to salt (but not water!) As filtrate ascends the thin segment of the ascending limb, NaCl is reabsorbed by passive transport from filtrate into vasa recta NaCl is further reabsorbed in thick segment, this time by active transport from filtrate into vasa recta Thin segment By losing salt without giving up on water along ascending limb, the filtrate becomes more dilute as it moves up to the renal cortex After active transport of NaCl out of thick segment of ascending limb, osmolarity of the filtrate changes from 1,200 mOsm/L to 100 mOsm/L (so filtrate in nephron is hypo-osmotic to the blood) Distal Convoluted Tubule The distal tubule regulates the K+ and NaCl concentrations of + body fluids by varying the amount of K that is secreted into the filtrate and the amount of NaCl reabsorbed from the filtrate Like the proximal convoluted tubule, the distal convoluted tubule reabsorbs water and also contributes to pH regulation by + controlled secretion of H and the reabsorption of HCO3 Osmolarity of the filtrate at end of distal convoluted tubule is 300 mOsm/L (so filtrate in nephron is iso-osmotic to the peritubular capillaries) Collecting Duct The collecting duct carries filtrate through the medulla to the renal pelvis At the outer medulla, the transport epithelium of the collecting duct plays a large role in determining how much salt is actually excreted in the urine by actively reabsorbing NaCl At the inner medulla, water is reabsorbed by osmosis but NaCl cannot reabsorb since transport epithelium is impermeable to salt – This concentrates salt, urea, and other solutes in the filtrate In the inner medulla, the collecting duct also becomes permeable to urea; but most of the urea in the filtrate remains in the collecting tubule The reabsorption of some urea and salt contributes to the high osmolarity of the interstitial fluid in the renal medulla Ideally, urine is hyper-osmotic to body fluids (in the collecting tubule, the osmolarity changes from an initial 100 mOms/L to 1,200 mOsm/L) 180 L of initial filtrate produced per day by human kidneys but about 99% of filtrate is reabsorbed – so, only a tiny fraction of the original volume is excreted Hormonal circuits link kidney function, water balance, and blood pressure Mammals control the volume and osmolarity of urine by nervous and hormonal control of water and salt reabsorption in the kidneys Antidiuretic hormone = ADH increases water reabsorption in collecting ducts of kidney ‒ ADH is produced in brain, and released into blood circulation before arriving at kidneys ‒ When blood osmolarity rises above 300 mOsm/L, more ADH is released into bloodstream and reaches kidney ‒ ADH causes epithelium of collecting ducts to become more permeable to water due to increased number of aquaporin water channels embedded in cell membrane (this increases water reabsorption) ‒ This reduces urine volume, which means that the urine is now more concentrated with salts Therefore, ADH can assist in regulating blood pressure by regulating blood volume. Where does reabsorption of glucose occur in the nephron? A. Bowman’s capsule B. Proximal convoluted tubule C. Loop of Henle D. Distal convoluted tubule E. Collecting duct Where does reabsorption of glucose occur in the nephron? A. Bowman’s capsule B. Proximal convoluted tubule C. Loop of Henle D. Distal convoluted tubule E. Collecting duct The descending loop of Henle in the nephron is permeable to which of the following substances? A. Potassium ions B. Sodium ions C. Water D. + H ions The descending loop of Henle in the nephron is permeable to which of the following substances? A. Potassium ions B. Sodium ions C. Water D. + H ions Numbers represent osmolarity [milliosmoles of solute (mOsm) per liter] Which parts of the nephron are mainly found in the renal medulla of the kidney? A. The entire nephron can be found within the renal medulla B. The loop of Henle and the collecting duct C. The proximal and distal convoluted tubules D. The loop of Henle and Bowman’s capsule Which parts of the nephron are mainly found in the renal medulla of the kidney? A. The entire nephron can be found within the renal medulla B. The loop of Henle and the collecting duct C. The proximal and distal convoluted tubules D. The loop of Henle and Bowman’s capsule Urine passes through all the following structures except the __________? A. ureters B. vasa recta C. urethra D. renal pelvis Urine passes through all the following structures except the __________? A. ureters B. vasa recta C. urethra D. renal pelvis The efferent arteriole leads oxygenated blood to the glomerulus while the afferent arteriole leads oxygenated blood away from the glomerulus. The efferent arteriole leads oxygenated blood to the glomerulus while the afferent arteriole leads oxygenated blood away from the glomerulus. afferent = arrives False The AFFERENT arteriole leads oxygenated blood to the glomerulus while the EFFERENT arteriole leads oxygenated blood away from the glomerulus. efferent = exits Does antidiuretic hormone primarily act on what part of the kidney to increase water reabsorption? A. Bowman’s capsule B. Proximal convoluted tubule C. Loop of Henle D. Collecting duct Does antidiuretic hormone primarily act on what part of the kidney to increase water reabsorption? A. Bowman’s capsule B. Proximal convoluted tubule C. Loop of Henle D. Collecting duct Filtration is the first step in urine formation and occurs in the distal tubule of the nephron. Filtration is the first step in urine formation and occurs in the distal tubule of the nephron. False Filtration is the first step in urine formation and occurs in the renal corpuscle What is the functional unit of the kidney responsible for filtering blood and producing urine? A.Urethra B.Ureter C.Nephron D.Bladder What is the functional unit of the kidney responsible for filtering blood and producing urine? A.Urethra B.Ureter C.Nephron D.Bladder What is the role of the antidiuretic hormone (ADH) in the excretory system? A. Promoting water reabsorption in the kidney. B. Enhancing urine production in the bladder. C. Stimulating urea synthesis in the liver. D. Regulating blood pressure in the heart. What is the role of the antidiuretic hormone (ADH) in the excretory system? A. Promoting water reabsorption in the kidney. B. Enhancing urine production in the bladder. C. Stimulating urea synthesis in the liver. D. Regulating blood pressure in the heart. Which blood vessel forms the glomerulus? A.Afferent renal arteriole B.Efferent renal arteriole C.Vasa recta D.Renal vein Which blood vessel forms the glomerulus? A.Afferent renal arteriole B.Efferent renal arteriole C.Vasa recta D.Renal vein afferent = arrives efferent = exits In what region of the nephron does the reabsorption of NaCl happen only through active transport? A.Descending limb of the loop of Henle B.Thin ascending limb of the loop of Henle C.Thick ascending limb of the loop of Henle D.Proximal tubule In what region of the nephron does the reabsorption of NaCl happen through passive transport? A.Descending limb of the loop of Henle B.Thin ascending limb of the loop of Henle C.Thick ascending limb of the loop of Henle D.Proximal tubule (4 marks( Label the parts of the nephron. A= B= C= D= E= F= G= H= (4 marks) Label the parts of the nephron. A = Proximal convoluted tubule B = Bowman’s capsule C = Glomerulus D = Distal convoluted tubule E = Descending arm (of loop of Henle) F = Ascending arm – thin segment (of loop of Henle) G = Ascending arm – thick segment (of loop of Henle) H = Collecting duct (1.5 marks) List the three processes that kidneys use to produce urine. (1.5 marks) List the three processes that kidneys use to produce urine. Filtration Reabsorption Secretion (1 mark) List the two parts of the renal corpuscle. (1 mark) List the two parts of the renal corpuscle. Glomerulus Bowman’s capsule (2.5 marks) Determine if the filtrate labelled in each red box is either iso-, hyper-, or hypo-osmotic to the blood. D A B C E (2.5 marks) Determine if the filtrate labelled in each red box is either iso-, hyper-, or hypo-osmotic to the blood. A B C D E Numbers represent osmolarity [milliosmoles of solute (mOsm) per liter] (2 marks) Explain how urea reabsorption in the nephron collecting duct affects the inner medulla's osmolarity and explain its importance for water reabsorption in the nephron. (2 marks) Explain how urea reabsorption in the nephron collecting duct affects the inner medulla's osmolarity and explain its importance for water reabsorption in the nephron. Reabsorption of urea maintains the high osmolarity of the inner medulla (1 mark). The high osmolarity in the inner medulla is important because it creates the concentration gradient that drives water reabsorption in the descending limb of the loop of Henle (1 mark). (5 marks) During urine production, its osmolarity changes depending on the nephron region. Describe the changes in urine osmolarity throughout the nephron and compare it with human blood osmolarity, which is 300mOS. (5 marks) During urine production, its osmolarity changes depending on the nephron region. Describe the changes in urine osmolarity throughout the nephron and compare it with human blood osmolarity, which is 300mOS. (5 marks) During urine production, its osmolarity changes depending on the nephron region. Describe the changes in urine osmolarity throughout the nephron and compare it with human blood osmolarity, which is 300mOS. The proximal convoluted tubule is the first region after the process of filtration. In this part, nutrients, water, and NaCl are reabsorbed back into the blood, and nitrogenous compounds and hydrogen ions are secreted into the urine (0.5 marks). This results in iso-osmotic urine compared to blood (300 mOsm) (0.5 marks). The descending limb of the loop of Henle is only permeable to water, and the reabsorption of water without movement of solute leads to an increase in urine osmolarity (0.5 marks), reaching 1200 mOsm, making urine hyper-osmotic compared to blood (0.5 mark). During the ascending limb of loop of Henle, NaCl is reabsorbed without water movement, first through diffusion (thin portion), then through active transport (thick portion) (0.5 marks). This decreases urine osmolarity until it reaches around 100 mOsm, making the urine hypo-osmotic compared to blood (0.5 marks). In the distal convoluted tubule, active secretion of hydrogen and potassium ions into the urine and reabsorption of water and NaCl back into the blood (0.5 mark). This results in iso-osmotic urine compared to blood (300 mOS) (0.5 mark). In the collector duct, water reabsorption can vary depending on the system's water balance (0.5 mark). Therefore, urine osmolarity can also vary from 300 to 1200 mOS, being iso-osmotic or hyper-osmotic compared to blood (0.5 mark).